1. Field of the Invention
The present invention relates to a gold wire for semiconductor element connection, used for electrical connection of external leads and the like to electrodes on semiconductor elements. Specifically, it relates to a gold wire for semiconductor element connection suitable for narrow pitch connections and thin electrode connections.
2. Description of the Related Art
Among the common methods of connecting external leads to semiconductor element electrodes, during mounting of semiconductor devices, are wiring methods such as ball bonding using gold wire, and methods of using gold wire to form bumps for connection through the bumps.
In wiring methods involving ball bonding, the gold wire is fed out and introduced into a capillary used as the bonding tool and then, after forming a ball at the tip of a fine metal wire projected from the opening of the tool, the ball is pressed against an Al electrode of the semiconductor element and the capillary is moved in the X, Y and Z directions (back and forth, left and right, up and down) to form a prescribed loop shape; after bonding to the external lead, the metal fine wire is then cut to accomplish wire bonding (this will hereunder be referred to as xe2x80x9cball bondingxe2x80x9d).
In methods of forming connections through bumps, the ball is pressed against the Al electrode of the semiconductor element and then the gold wire is cut near the ball attachment base, to form a connection through the ball (this will hereunder be referred to as xe2x80x9cbump connectionxe2x80x9d).
With the higher performance and size reduction of semiconductor devices in recent years, advances are being made in reducing pitches due to the increase in pin numbers of semiconductor elements. This has raised the level of performance demanded of gold wires and, because the outer diameter of the press bonded balls obtained by pressing the balls is about twice the diameter of the wire, one of the important properties of performance required is to improve the roundness or circularity of the press bonded balls.
It has been attempted in the past to control the roundness of the ball before press bonding during their formation. However, in recent years it has been found that the roundness of press-bonded balls which are suited for narrow pitch connections does not necessarily match the roundness of the non-press-bonded balls.
Preliminary attempts to improve the roundness of press-bonded balls have therefore been proposed. For example, Japanese Unexamined Patent Publication HEI No. 11-163016 discloses adding at least one from among Cu, Pt and Pd in a total of 0.03-5 wt %, Japanese Unexamined Patent Publication HEI No. 10-172998 discloses adding Be and Ca, and Japanese Unexamined Patent Publications HEI No. 10-303239 and HEI No. 10-83716 disclose adding Ca or the like in addition to Mn and Pd.
For narrow pitch wiring, however, the balls used for press bonding are more minute than conventional balls, and their roundness must be maintained after press bonding for smaller press bonded sizes. Among the techniques mentioned above, the disclosure of Japanese Unexamined Patent Publication HEI No. 10-172998 has a drawback in that minute balls have insufficient press bonded roundness, or the prescribed wire strength cannot be achieved. With narrow pitch connections in wiring bonding, it is particularly important to improve the wire strength to prevent contact shorts due to wire failure.
The other techniques also have drawbacks, such as insufficient press bonded roundness of minute balls, or high electrical resistance as a result of the vastly increased contents of elements added to improve the roundness.
In addition, with the demand for thin-film Al electrodes in schematic elements, and thinner sizes of these electrodes, electrode breakage occurs, due to the press bonded balls, particularly in the case of bump connections, thus leading to the problem of semiconductor element, or IC, chip cracking (hereunder referred to as xe2x80x9cchip crackingxe2x80x9d). The drastic increase in the content of added elements as mentioned above is also implicated in the problem of chip cracking.
Furthermore, when a connection is established by a bump, a method is adopted wherein the gold wire is pulled upward after the ball has been pressed onto the Al electrode of the semiconductor element, to cause a break near the base of the ball. Here, it is necessary to achieve a uniform length for the remaining wires attached to the press bonded balls (hereunder referred to as xe2x80x9ctail lengthxe2x80x9d).
It is an object of the present invention, which has been accomplished in light of these circumstances of the prior art, to provide a gold wire for semiconductor element connection which has a specific gold alloy composition with an added element content of no greater than 200 ppm by weight in order to minimize increase in electrical resistance, and which improves the roundness after press bonding of minute balls, exhibits high wire strength, produces no problem of chip cracking due to the press bonded balls even in the case of a small Al electrode film thickness on a semiconductor element, and gives a uniform tail length for bump connections.
The present invention provides the following in order to achieve the aforementioned objects.
(1) A gold wire for semiconductor element connection consisting of 5-100 ppm by weight of Ca, 5-100 ppm by weight of Gd and 1-100 ppm by weight of Y, the total amount of these elements being no greater than 200 ppm by weight, the balance being gold and unavoidable impurities.
(2) The gold wire for semiconductor element connection according to (1) above, which further consists of 1-100 ppm by weight of at least one from among Mg, Ti and Pb, the total amount of the added elements being no greater than 200 ppm by weight.
(3) A gold wire for semiconductor element connection consisting of 5-100 ppm by weight of Ca, 5-100 ppm by weight of Gd, 1-100 ppm by weight of Y, and 1-100 ppm by weight of at least one from among rare earth elements other than Gd and Y, the total amount of these elements being no greater than 200 ppm by weight, the balance being gold and unavoidable impurities.
(4) The gold wire for semiconductor element connection according to (3) above, which further consists of 1-100 ppm by weight of at least one from among Mg, Ti and Pb, the total amount of the added elements being no greater than 200 ppm by weight.
(5) A semiconductor element connection method which comprises
(A) a step of inserting a gold wire into a capillary, and heating and melting the tip of the gold wire to form a gold ball,
(B) a step of lowering the capillary and pressing the gold ball against an electrode of the semiconductor element to bond the gold wire to the electrode,
(C) a step of tracing a prescribed path with the capillary including the gold wire bonded to the electrode, to move it over a member to be connected and establish a press bond between the side of the gold wire and the member to be connected, and
(D) a step of raising the gold wire which has been press bonded to the connection member while clamping it with a damper to cut the gold wire, to complete wiring of the gold wire between the semiconductor element electrode and the connection member, wherein the gold wire is a gold wire according to any one of (1) to (4) above.
(6) The method of (5) above, wherein step (A) and/or step (C) further includes transmitting ultrasonic vibrations through the capillary to the gold wire tip while heating the semiconductor element or connection member with a heater block for thermocompression bonding of the gold ball.
(7) The method of (5) or (6) above, wherein the pitch of the adjacent electrodes on the semiconductor element is no greater than 70 xcexcm.
(8) The method of (5) or (6) above, wherein the pitch of the adjacent electrodes on the semiconductor element is no greater than 60 xcexcm.
(9) A semiconductor element connection method which comprises
(A) a step of inserting a gold wire into a capillary, and heating and melting the tip of the gold wire to form a gold ball,
(B) a step of lowering the capillary and pressing the gold ball against an electrode of the semiconductor element to form a press bonded gold ball, and
(C) a step of raising the gold wire which has the formed press bonded gold ball on the semiconductor element electrode while clamping it with a damper to cut the gold wire near the base of the press bonded gold ball, to form a bump on the electrode, wherein the gold wire is a gold wire according to any one of (1) to (4) above.
(10) The method of (9) above, which further comprises a step of press bonding the bump formed on the semiconductor element electrode to a member to be connected.
(11) The method of (9) or (10) above, wherein step (A) further includes transmitting ultrasonic vibrations through the capillary to the gold wire tip while heating the semiconductor element with a heater block for thermocompression bonding of the gold ball.
(12) The method of any one of (9) to (11) above, wherein the semiconductor element electrode is an aluminum electrode film with a film thickness of no greater than 0.5 xcexcm.
(13) The method of any one of (9) to (11) above, wherein the semiconductor element electrode is an aluminum electrode film with a film thickness of no greater than 0.1 xcexcm.